 |
Melilotus albus
Medik. [With some information on Melilotus officinalis - Yellow Sweet Clover - Photo] |
|||||||||||||||||||||||||
 
|
COMMON NAMES White sweetclover, White melilot, Bokhara clover |
Author: Dr.
John Frame |
||||||||||||||||||||||||
DESCRIPTION Erect or ascending biennial, up to 1.5 m, with trifoliate leaves . Leaflets obovate, dentate in upper third and with terminal leaflet on longer petiole than lateral leaflets (a feature used to differentiate the plant from alfalfa , since both species have a similar appearance in the vegetative state). Single well-branched stem in establishment year but several stems originate from crown buds in following year. The succulent stems become fibrous with age. Deeply tap-rooted. Considerable root enlargement together with short rhizomes initiated from the plant crown take place in autumn of the establishment year. In contrast, annual sweetclovers have more aboveground forage and less root development in the year of sowing. Inflorescences are elongated one-sided racemes of white flowers, 4–5 mm,
borne on long axillary stalks. Indeterminate flowering, self-fertile.
Seed pod has a reticulated, ridged coat which turns black with ripening
and contains a single smooth, kidney-shaped seed, about 2 mm long,
and brownish-yellow to brown. There is a high content of hard seed in
harvested crops. In DISTRIBUTION It is indigenous to central Europe, eastern Mediterranean countries and northwest Asia, and introduced to many other temperate regions, but mainly used in North America, including use under irrigation , though its use there has declined in recent years. White sweetclover is the most commonly grown species of the genus, followed by yellow sweetclover (Smith and Gorz, 1965; Miller and Hoveland, 1995). Table 1. Melilotus species listed in the PLANTS database (2000), and equivalent European names.
Note:
Annual yellow sweetclover was referred to as King Island melilot or
sour clover in The following refers to biennial white sweetclover as representative of the genus, but with some reference to other sweetclovers, particularly biennial yellow sweetclover . CHARACTERISTICS Growth It is adapted to a wide range of soils but not to acidic soils, and tolerant of alkaline and saline soils. It responds to high fertility, particularly of P and K. Optimum pH range is 6.5–7.5 (PLANTS database, 2000). It has moderate seedling vigour, with a spring to autumn growth season. Shows vigorous growth in year after establishment and where previous autumn management has allowed plants to develop strong root systems with good carbohydrate and N reserves. It is intolerant of shade, and has a low tolerance of flooding. There is a high degree of drought tolerance once established, though yellow sweetclover is considered to be more drought tolerant. While a winter hardy species, utilization in the autumn of the establishment year can result in subsequent winter kill if there has been insufficient time for build up of root reserves. Yellow sweetclover exhibits good frost resistance (Brandsaeter et al., 2002). Ability to spread naturally Poor, although it does spread by seed and frequently appears as a weed in disturbed areas in regions where it was previously used and allowed to go to seed. Nitrogen fixation It requires seed inoculation by an effective
strain of Rhizobium meliloti for successful establishment
and performance. For example, at a site in Alaska, BREEDING Self-fertile, pollinated mainly by honey bees (Apis mellifera). Chromosome number 2n=2x=16 (biennial yellow sweetclover is cross-pollinated). Breeding objectives in the past were low coumarin content, increased forage yield, improved characteristics for grazing , and better disease and pest resistance, but currently there is very little breeding work with this plant. Cultivars Smith and Gorz (1965) noted that much of the seed
on the market was of the unimproved, common type rather than specific
cultivars. Nevertheless they listed 12 biennial cultivars of M. alba
, with a range of maturity classes, and five annuals, mostly released
in the Seed production For best results, seed crops are cut and windrowed when about half the seed pods have become brown to black (Smith and Gorz, 1965); seed loss can be substantial because of weak attachment of pods and pod shatter during combining. Crops can also be directly combined following application of a crop desiccant. Average seed yields are about 225 kg ha-1 (Miller and Hoveland, 1995). AGRONOMY Establishment A well-cultivated, uniform and firm seed bed is required for good results. Seed is usually drilled or broadcast directly after conventional seedbed cultivations, but can also be sown under a cereal cover crop . Optimum seed depth is 15–20 mm, with a firm soil cover. Direct drilling (sod seeding) into the existing grass sward can also be practised. Although usually sown in spring, it can also be sown in early autumn. Seed is normally scarified before sowing. Seed rates are 9–12 kg ha-1 for scarified seed when sown pure, but reduced to 4–5 kg ha-1 if sown in mixture with grasses such as Bahia grass (Paspalum notatum) or perennial ryegrass (Lolium perenne). Nutrient requirements Adequate soil fertility is required to ensure satisfactory yields . Weeds Its ability to compete with weeds is moderate during early establishment but improves with time as the legume canopy develops. It tolerates ‘legume-safe’ herbicides, but not less selective types. Pests Sweetclover weevil (Sitona cylindricollis) is a major pest at establishment and infestations can also damage established stands. Other pests are the root-borer (Walshia miscecolorella), blister beetles (Epicautua spp.) and aphid (Therioaphis riehmi). Diseases Sweetclover may be affected by a number of diseases , the main ones being clover rot (Sclerotinia trifoliorum), spring black stem (Ascochyta meliloti), summer black stem (Cercospora davisii), stem canker (Ascochyta caulicola) and root rot (Phytophthora cactorum). Viruses A number of viruses can cause subclinical or clinical damage. Forage production Hay yields up to 7–8 t ha-1
are achievable. In Alaska, NUTRITIVE VALUE It has a high nutritive value at the vegetative stage of growth when grazed, at pre-flowering stage for silage , and at early-flowering stage for hay. Compared with red clover , biennial yellow sweetclover had lower N content and higher cell wall and lignin contents in the stems , but higher N contents in the leaves (Wivstad, 1997). It has good acceptability after stock have become used to the bitter taste caused by the coumarin content of the forage. Anti-quality factors There is risk of bloat. The feeding of hay or silage spoiled by the development of moulds, due to aeration and heating, produces an anti-coagulant from the coumarin content, which can cause ‘bleeding disease’ – hence the past development of low-coumarin cultivars. UTILIZATION Grazing management Lax defoliation by grazing in late autumn of establishment year encourages good root development. Lax grazing is also necessary in the harvest year since regrowths emerge from buds on the lower parts of the stems , but grazing has to be sufficiently severe to prevent stems becoming mature and coarse. Conservation management Stands are mainly grazed, though also suitable for forage conservation. Careful handling during hay making is necessary to minimize loss of nutritious leaf. MAIN ATTRIBUTES It provides high forage yields suitable for grazing and conservation. It is drought tolerant, winter hardy and tolerant of alkaline soils. MAIN SHORTCOMINGS It is susceptible to sweetclover weevil attack during early establishment, and prone to a number of diseases. There is risk of bloat, and of livestock bleeding disease from mouldy hay or silage. MAIN REFERENCES Miller and Hoveland (1995); Smith and Gorz (1965). OTHER REFERENCES McEwen J. and Johnston A.E. (1985); Panciera M.T. and Sparrow S.D. (1995); Plants Database 2000; Sparrow S.D. et al.(1993); Wivstad M. (1997); Zimmermann L.R. et al.(1998) LINKS
|
||||||||||||||||||||||||||